1. Field of the Invention
The present invention relates to a position measuring device, having a first element and a second element, wherein the first element can be displaced in relation to the second element. The present invention further relates to a method for position measuring by such a position measuring device. Finally, the present invention furthermore relates to a processing machine, in particular a machine tool.
2. Discussion of Related Art
Such position measuring devices often include a first component, for example a scale housing, in which a scale, or a measuring tape as a material measure, is housed, and of a second component, often a scanning carriage with a scanning head, by which scanning of the material measure is performed. Both components can be displaced in the measuring direction in relation to each other and can be mounted on respective elements, which can be displaced in relation to each other, of a processing machine, for example a machine tool, in order to determine the relative position of these elements which are displaceable with respect to each other.
In the course of operating such machine tools, heat is introduced into the machine tool, which comes from the drive mechanisms, bearings or guide devices. This heating leads to thermal expansions and deformations of the machine tool and is also transmitted to the material measure as a rule, so that a temperature-related length change can also be noted there. Thus, this heating in the end results in an interference with the processing accuracy of the entire machine tool.
There have been a large number of attempts to reduce the deterioration of the processing accuracy, for example by a matching construction of the machine tool. However, these offer only a limited optimization potential, so that often an active, temperature-dependent correction of the measured values is performed.
In DE 199 04 472 A1 of Applicant, an improved correction of temperature-dependent deformations of machine tools is achieved by a special placement of elongated temperature sensors. There, the evaluation of the temperature sensor signals takes place in the numerical control of the machine tool.
In accordance with DE 100 07 540 A1, the temperature gradient along a scale can be used for a temperature correction of a linear measurement. In this case the measured data from point-shaped individual sensors are appropriately processed.
A position measuring device is represented in DE 196 01 275 A1 of Applicant, wherein the local scale temperature is determined by a temperature sensor moved along with the scanning carriage. The corresponding temperature signal is transmitted via a cable to a stationary electronic device, in which a corrected position value is calculated.
The devices and methods of the prior art have, inter alia, the disadvantage that an alignment between the electronic evaluation device, which is customarily housed in the numerical machine control, and the position measuring device is required for a thermal correction. Incompatibilities often occur in the course of this, which in most cases can be removed only with a great expenditure of time, if at all.